Chemical Analysis of Slag

Production debris can be found in large amounts during archaeological excavations, but it is not always fully appreciated exactly how much information can be extracted from such un-prepossessing material (Bayley et al. 2008). Funding large-scale analytical programs is often difficult but in cases where development-led archaeology has funded the analysis of metallurgical material, the results have been well worthwhile (Niblett 1999).

Research Questions and Answers

Chemical analysis is seen as the way to address questions of ore source by characterising slag according to compositional profile, and matching this to either slag of known origin or metal ores from known mines. Recent work suggests the composition of iron slags is related to that of the ores smelted (Buchwald & Wivel 1998; Paynter 2006). This is particularly suitable and/or necessary if there are two possible ore sources and a need to distinguish between them.

A combination of visual examination and scientific analysis can also indicate the variability within a slag assemblage, and hence inform decisions about the discard or dispersal of some of the material often a welcome relief to museum professionals with over-full stores (Bayley et al. 2008).

Finally, there is a potential that slag that has been chemically analysed can be used in slag inclusion studies to trace iron used in artefacts to their smelting sites (Blakelock et al. 2009). This is particularly important when there is evidence for smelting and smithing, and also when stock iron is found on the same site. This analysis will primarily provide answers about the sites trade networks.

Costs

Scanning electron microscopy (SEM), usually with an energy dispersive analysis system (EDS) is a very versatile imaging and micro-analysis technique which is becoming increasingly common in archaeological studies. This technique is particularly well suited to archaeological material, especially process residues, as it relates composition to structure, and allows the chemical analysis of particular areas or phases, as well as providing bulk compositions. A small fragment will be taken from the selected slag this will need to be prepared before any analysis can take place.

Therefore the cost of chemical analysis of slag is approximately £240 per sample. It is generally beneficial to analyse more than one sample to reduce variability. This analysis will also include comparison with contemporary slag from relevant geographical areas. Discounts can be provided for large sample sets. There may be discounts for charity/amateur groups or assemblages that fit within my research interest.